The present invention relates to a convergence apparatus in a color CRT display.
Heretofore, in a color CRT display for selecting displaying colors by a plurality of electron beams, it has been proposed to attain the horizontal and vertical convergence corrections of the electron beams by using an apparatus comprising horizontal convergence coils for generating a horizontal convergence correction magnetic field and vertical convergence coils for generating a vertical convergence correction magnetic field and to feed horizontal and vertical convergence correction currents to the two coils for each of the pole pieces which impart electromagnetic action to the electron beams, respectively.
FIG. 1 shows the structure of one pole piece in the conventional convergence apparatus.
FIG. 2 shows current waveforms for illustrating the conventional convergence apparatus.
In FIG. 1, the reference numeral 1 designates a pole piece; 2 designates a vertical convergence coil; 3 designates a horizontal convergence coil. In the apparatus, the sawtooth waveform voltages V.sub.1, V.sub.2 which are respectively proportional to the vertical and horizontal deflecting currents of the vertical and horizontal convergence coils 2, 3 are applied to pass parabolic waveform currents I.sub.1, I.sub.2 shown in FIG. 2 which are formed by the integrating action of the convergence coils, thereby providing a suitable convergence correction magnetic field.
However, in the conventional apparatus, both of the vertical and horizontal convergence coils 2, 3 connected to each pole piece are disposed in close electromagnetic coupling. Accordingly, when the current waveform in one convergence coil is varied, the variation affects that of the other convergence coil whereby the convergence alignment is not easily attained.